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Study on preparation of Ca/Al/Fe3O4magnetic composite solid catalyst and itsapplication in biodiesel transesterication

Shaokun Tang , Liping Wang, Yi Zhang, Shufen Li, Songjiang Tian, Boyang WangKey Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering & Technology, Tianjin University, Tianjin, 300072, China

a b s t r a c ta r t i c l e i n f o

Article history:

Received 19 July 2011

Received in revised form 12 November 2011Accepted 26 November 2011Available online 24 December 2011

Keywords:

MagneticFe3O4nanoparticlesSolid base catalystBiodieselTransesterication

A magnetic composite solid catalyst was prepared by loading calcium aluminate onto Fe3O4nanoparticles viaa chemical synthesis method. The optimum conditions for the catalyst preparation were investigated. The in-uences of the molar ratio of Ca to Fe, calcining temperature, calcining time on the catalytic performancewere studied. The catalyst with the highest activity was obtained when the molar ratio of Ca to Fe was 5:1;calcining temperature was 600 C and calcining time was 6 h. The catalyst was characterized by thermogravi-metric analyses (TGA),X-ray diffraction (XRD),scanning electronic microscope (SEM),BrunauerEmmettTellermethod (BET) and vibrating sample magnetometer (VSM). Furthermore, the magnetic composite solid catalystshowed high catalytic activity for transesterication reaction for preparing biodiesel and the biodiesel yieldreached98.71% underthe optimumconditions. The activity andrecovery rateof thismagneticcompositecatalystcan be well maintained after 5 cycles of catalysis. This catalyst showed magnetism and can be easily separatedmagnetically. Both the catalytic activity and the recovery rate of the magnetic composite solid catalyst weremuch higher than those of pure calcium aluminate catalyst.

2011 Elsevier B.V. All rights reserved.

1. Introduction

Biodiesel has attracted attention in recent years as a renewablebiofuel with less pollutant emissions compared to mineral diesel onits combustion[1,2]. Transesterication is the most common methodfor biodiesel preparation. Most biodiesel today is produced in thepresence of homogeneous catalysts such as sodium methoxide, sodiumor potassium hydroxide [3]. Freedman et al. [4] reported thatNaOH cantransform vegetableoil to biodiesel completely in an hour. But their dis-advantages are the complicated processes of post treatments andpollution.

In this case, researches have focused on nding a suitable hetero-geneous catalyst that can be easily separated and give a high yieldand conversion without compromise[5].Since the catalytic activityof basic catalysts is higher than that of acid solids, they have been

preferably studied. Heterogeneous solid base catalysts have beenpresently reported such as metal oxides CaO [6-9], SrO[10]and soon; alkali-doped metal oxides KF/MgO[11], CaO/Al2O3 [12], MgO/Al2O3 [12], Li/CaO [13], CaO/ZnO [14] and so on; supported ones,such as Na/NaOH/-Al2O3 [15] and KF/-Al2O3 [16]; hydrotalcitesMgAl [1719], KF/hydrotalcite[20], KF/CaMgAl hydrotalcite[21]and so on; sodium aluminate[22], SnCl2[23], calcium ethoxide[24]and mayenite [25]. Although these heterogeneous catalysts have

advantages in catalyst separation and pollution reduction, most of

them have some limitations in catalytic activity and stability.The heterogeneous base catalyst for biodiesel preparation hasbeen developed in our group. Heterogeneous base catalyst K/KOH/-Al2O3was prepared and used in the transesterication of rapeseedoil with methanol to produce biodiesel[26]. The result showed thatthe catalyst K/KOH/-Al2O3had high catalytic activity and the yieldof biodiesel could reach as high as 84.52% after 1 h reaction at 60 C,with a 9:1 molar ratio of methanol to oil, a catalyst amount of4 wt.%. However, after two-times use, it was found that the biodieselyield decreased to 37.6%, and the catalyst lost weight of 10.8%, whichmeant the relatively low stability and recovery rate of the catalyst.Therefore, the development of a heterogeneous catalyst with highactivity and stability is still in high demand.

Nanometer magnetic solid base catalyst can be separated easily

from the reagents by an external magnetic

eld, which can effectivelyprevent catalyst loss and improve its recovery rate during separationprocess. Furthermore, magnetic nanoparticlessupported solid catalystshow high dispersion so as to contact reactants more sufciently basedon the high surface area of the supported magnetic nanoparticles.Nanometer magnetic catalyst has been attracting more and more in-creasing attention in recent years. Fe3O4magnetic particles were usedto immobilize lipase as catalyst for biodiesel production. The resultsshowed not only high catalytic activity but also the advantages of easyseparation and reuse [27,28]. Hu et al . [29] developed a nano-magnetic solid base catalyst KF/CaOFe3O4based on Fe3O4magneticcore by impregnation method. The catalyst recovery was more than90%. When the reaction was carried out at 65 C with a methanol/oil

Fuel Processing Technology 95 (2012) 8489

Corresponding author. Tel./fax: +86 22 27408578.E-mail address:[email protected](S.K. Tang).

0378-3820/$ see front matter 2011 Elsevier B.V. All rights reserved.

doi:10.1016/j.fuproc.2011.11.022

Contents lists available at SciVerse ScienceDirect

Fuel Processing Technology

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / f u p r o c
http://dx.doi.org/10.1016/j.fuproc.2011.11.022http://dx.doi.org/10.1016/j.fuproc.2011.11.022http://dx.doi.org/10.1016/j.fuproc.2011.11.022mailto:[email protected]://dx.doi.org/10.1016/j.fuproc.2011.11.022http://www.sciencedirect.com/science/journal/03783820http://www.sciencedirect.com/science/journal/03783820http://dx.doi.org/10.1016/j.fuproc.2011.11.022mailto:[email protected]://dx.doi.org/10.1016/j.fuproc.2011.11.022


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molar ratio of 12:1 and a catalyst concentration of 4 wt.%, the biodieselyield exceeded 95% at 3 h of reactiontime. Liu et al. [30] prepared nano-meter magnetic solid base catalysts for transesterication reaction byloading CaO on Fe3O4with Na2CO3and NaOH as precipitator, respec-tively. The conversion rate of transesterication reaction catalyzed bynanometer magnetic solid base catalysts under optimum conditionscould reach 95% in 80 min, and to 99% in 4 h. Fatty acid methyl esters(FAME) yield was more than 90% after 5-times use and still more than

70% after 10-times use. Therecovery rate of the Ca(OH)2

Fe3O4 catalystafter reaction reached up to 91.45%. According to Scherer formulaD=0.89/cos, the average particle diameter was calculated to be49.76 nm. But the BET specic surface area of this catalyst was only3.72 m2/g and the saturation magnetization of magnetic catalysts wassmaller than 1 eum/g.

In our work, calcium aluminate catalyst has been developed via achemical synthesis method for transesterication reaction of biodieselproduction. Furthermore, the magnetic composite solid catalyst hasbeen prepared by loading calcium aluminate onto the nanometerFe3O4to improve the catalytic performance including the catalyticactivity and recovery in application to biodiesel preparation.

2. Experimental section

2.1. Materials

Rapeseed oil was purchased from Ningbo zhengda grain and oilCompany. Sodium hydroxide, methanol, Al, CaCO3, absolute alcoholand isopropanol were analytical grade, obtained from Tianjin JiangtianChemical Reagent Company, China. Fe3O4(99.5%, 20 nm spherical par-ticles) was purchased from Shanghai Yutian Chemical Company.

2.2. Preparation of Ca/Al/Fe3O4magnetic composite catalysts

NaOH was solved into distilled water, and then aluminum sheetwas added into NaOH solution. After reaction, sodium meta-aluminate solution was obtained. CaO obtained by calcining of

CaCO3 at 1000 C for 10 h, and CaO was added into distilled water,then calcium hydroxide suspensions formed. The molar ratio ofNaOH, Al and CaO was 2:2:3. A certain amount of Fe3O4nanoparticleswas added into themixed solution of NaOH and Ca(OH)2 with vigorousstirring at 80 C for 5 h. The as-prepared powders were thoroughlywashed with deionized water, dehydrated using alcohol, and thendried under vacuum for 12 h. At last, the dried powder was calcinedto produce magnetic composite solid catalysts.

The inuences of the molar ratio of Ca to Fe, calcining tempera-ture and calcining time on FAME yield were investigated in thiswork. Besides, in order to compare the catalytic activity of the mag-netic composite solid catalyst with that of pure calcium aluminatecatalysts, the calcium aluminate catalysts were prepared in thesame way.

2.3. Transesterication for biodiesel

The transesterication of 67.5 g rapeseed oil was carried out in a250 ml round-bottom ask, provided with a thermostatic and mag-netic stirring system. In our previous study, the optimum transester-ication conditions catalyzed by calcium aluminate were obtained asfollows: methanol/oil molar ratio 15:1, catalyst dosage 6 wt.% of rape-seed oil, reaction temperature 65 C, the stirring rate of 270 rpm andreaction time of 3 h.

All the transesterication reactions in this paper were performedunder the obtained optimum conditions to determine the catalyticactivity of the catalysts. After reaction, the magnetic composite solidcatalysts were recycled by magnetic separation. A small amount of

the product mixtures was taken and washed with deionized water

at 70 C, centrifuged for 30 min. Then the sample taken from the oiphase was analyzed by gas chromatography.

2.4. GC and GC-MS analysis of FAME

The sample was taken from the oil phase and determined byGC (SP-2100) with capillary column of H.J.PEG-20M(30 m0.32 mm0.5m). To detect the yield of biodiesel, methyl

salicylate was used as internal standard, ethyl acetate as solvent. Thecolumn temperature was 130 C, the temperatures of the injector anddetector were respectably 180 C and 280 C. Programmed temperaturewas that initial temperature was 130 C remaining 3 min, the tempera-ture was elevated by 30 C/min to 190 C, then elevated by 5 C/min to230 C remaining 5 min.

The components of fatty acid methyl esters after transesterica-tion reaction were determined by GC-MS (6890-5973N, Aglient)The ion source of MS was electron ionization at 230 C with capillarycolumn of HP-INNOwax (30 m0.25 mm0.25 m). The interfaceand quadrupole temperatures were 250 C and 150 C respectively.The initial column temperature was 160 C remaining 2 min, andthen was programmed elevated by 5 C/min to 240 C remaining10 min. There were mainly seven components including methypalmiate, methyl stearate, methyl oleate, methyl linoleate, methyllinolenate, methyl cis-11-eicosenoate and methyl erucaterespectively.

The FAME yield was calculated by internal standard method usingthe following equation:

YieldFAME festerAester

Ainternal

minternalmesters

100%: 1

In formula(1),Aester is the peak area of fatty acid methyl esters,Ainternais the peak area of internal standard (methyl salicylate), minternalis themass of internal standard (methyl salicylate),mestersis the mass of fattyacidmethyl estersandfester is thecorrectionfactor of fatty acid methyl es-ters. The correction factors of methyl palmiate, methyl stearate, methyloleate, methyl linoleate, methyl linolenate, methyl cis-11-eicosenoate

and methyl erucate were determined as 0.8250, 1.1789, 0.8121, 0.81540.9556, 1.9434, 3.0437 respectively.

2.5. Characterization of the solid catalysts

The morphologies of the as-prepared calcium aluminate catalystsand magnetic composite solid catalysts were observed by scanningelectronic microscopy (SEM, Nanosem 430, FEI, USA). The thermalstability of catalyst was examined using thermogravimetric analyzer(TGA, TA-50, Shimadzu, Japan) from room temperature to 750 Cunder an inert nitrogen atmosphere and a heating rate o10 C min1. The magnetic hysteresis loops of the Fe3O4 particleswere measured with a vibrating sample magnetometer (VSM, LDJ9600, LDJ Electronics, USA) at room temperature under applied mag-

netic eld of 1T. X-ray diffraction analysis was carried out by usingan X'Pert PRD X-ray diffraction system (Philips X' pert, Cu K radia-tion k=1.54056 , USA). The specic surface areas of the catalystswere detected by the BET nitrogen adsorption method at 196 C(Tristar3000, Micromeritics, USA).

3. Results and discussion

3.1. Catalytic activities of magnetic composite solid catalysts

To explore the optimal conditions for catalyst preparation, differentmolar ratios (10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1 and 2:1) of Ca to Fe,calcining temperature (450 C, 500 C, 550 C, 600 C, 650 C, 700 C750 C and 800 C), calcining time (2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h and

9 h) were studied.

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3.1.1. Effect of molar ratio of Ca to Fe

The effect of n (Ca): n (Fe) on the FAME yield was studied whenthe calcining temperature was 600 C and calcining time was 6 h.Fig. 1indicated that the FAME yield increased with the increase ofthe molar ratio of Ca to Fe from 2:1 to 5:1. However, with the furtherincrease of the molar ratio of Ca to Fe from 5:1 to 10:1, the FAME yielddecreased. The FAME yield at the molar ratio of Ca to Fe 5:1 was thehighest, and also higher than that with pure calcium aluminate cata-

lysts (89.87%).XRD determination showed that the magnetic composite catalystafter calcination was the composite of Ca12Al14O33, CaO and Fe3O4(seen in Section 3.4.2). On one hand, with the increase of molarratio of Feto Ca, the relativecontentof Fe3O4 increases and the catalyticactive components Ca12Al14O33 and CaO for transesterication de-crease, and thus reduces the catalytic activity. On the other hand, dueto high specic area of the Fe3O4 nanoparticles supporter, the Ca/Al/Fe3O4 magnetic composite solid catalyst has larger specic surfacearea and thus shows higher dispersion in the reactantwith the additionof Fe3O4particles. The data of the specic surface areas of the catalystscan be seen in Section 3.4.4. As a result, the catalytic activity and the reac-tion yield will be promoted. Based on the above two competitive factors,the optimum molar ratio of Ca to Fe is 5:1.

3.1.2. Effect of calcining temperature

In this work, the calcining temperature varied within a range from450 C to 800 C at the molar ratio of Ca to Fe of 5:1 and calcining timeof 6 h. With the increase of calcining temperature, the catalyst gradu-ally develops into crystal and its specic area increases. The specicsurface area of the magnetic composite catalyst at 600 C was thehighest (25.89 m2/g) by BET determination. Correspondingly, the bio-diesel yield initially increased and reached the highest 98.71% whenthe calcining temperature was 600 C as seen inFig. 2. However, toohigh temperature (>600 C) results in the surface sintering and thereduction of specic surface area of the composite catalyst, whichleads to the decrease of the catalytic activities and the biodieselyield with the further increase of the calcining temperature. There-

fore, the optimum calcining temperature is 600 C.

3.1.3. Effect of calcining time

Fig. 3shows the effect of the calcining time on the yield of methylester when the molar ratio of Ca to Fe is 5:1 and the calcining temper-ature is 600 C. It can be found that the yield of methyl ester was thehighest 98.71% when magnetic catalysts were calcined for 6 h at600 C.

With the increase of the calcining time from 2 h to 6 h, the catalystgradually develops into stable crystal and the specic area of catalystincreases. As a result, the FAME yield increases and reaches the highestwhen the magnetic catalyst is calcined for 6 h. With the further increaseof the calcining time, part of active component of the catalysts maybe lost and catalyst agglomeration will happen, which results in thedecrease of the FAME yields. In our work, the calcining time of 6 his considered as the optimum.

In summary, Ca/Al/Fe3O4 magnetic composite catalyst with thehighest catalytic activity has been obtained when the molar ratio ofCa to Fe was 5:1, calcining temperature was 600 C and calciningtime was 6 h. All the as-calcined magnetic composite catalysts men-tioned in the following text were prepared under the optimum condi-tions. This magnetic composite catalyst can lead to a higher productyield 98.71% in the transesterication of biodiesel.

3.2. Determination of recovery rate of catalysts

After the transesterication reaction, the product mixtures withpure calcium aluminate catalyst or magnetic composite catalystwere respectively put in 2200 gauss magnetic eld for 0.5 h. Thenthe upper layer liquid was taken out and the remaining magneticmixture was washed with isopropanol three times, alcohol two

Fig. 1.Effect of n (Ca): n (Fe) on FAME yield. Calcining temperature 600 C; calcining

time 6 h.

Fig. 2.Effect of calcining temperature on FAME yield. Molar ratio of Ca to Fe 5:1; calciningtime 6 h.

Fig. 3.Effect of calcining time on FAME yield. Molar ratio of Ca to Fe 5:1 and calcining

temperature 600 C.

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times and then dried. The results showed that the recovery rate ofpure calcium aluminate catalyst was 80.81% while that of Ca/Al/Fe3O4magnetic composite catalyst was higher to 93.80%, which wasalso higher than that of Ca(OH)2Fe3O4 catalyst (91.45%) reportedin Ref. [30].

3.3. Reusability tests of catalysts

Catalyzed by Ca/Al/Fe3O4magnetic composite catalyst or pure cal-cium aluminate catalyst, transesterication of rapeseed oil withmethanol was respectively conducted several times under the samereaction conditions. The experiment continued for 3 h for every runand the tests repeated 5-times.Fig. 4showed that after 5-times use,the FAME yield reached to 93.53% and the recovery rate kept about87% for Ca/Al/Fe3O4magnetic composite catalyst. In comparison, theFAME yield decreased to 86.02% after 5-times and the recovery ratefor pure calcium aluminate catalyst was less than 70%. It indicatedthat the Ca/Al/Fe3O4 magnetic composite catalyst can be easilyrecycled with a little loss by magnetic eld and can maintain highercatalytic activity and higher recovery even after being used 5 timesthan pure calcium aluminate catalyst.

The change of reaction rate with reaction time at the ve recycles

is given inFig. 5. It can be found that the FAME yield decreased withrecycling times due to the loss of catalytic active components duringthe reaction and separation processes. Furthermore, the reaction ratekept fast in cycles 1 and 2 and high FAME yield can reach after 2 h.However, the reaction rate gradually decreased with the further recycleand high yield can be achieved after 3 h.

3.4. Catalyst characterization

3.4.1. Thermogravimetric analysis of catalyst precursor

The TG proles of the catalyst precursor with/without magneticnanoparticles are shown inFig. 6. Compared the thermogravimetricanalysis of pure calcium aluminate catalyst precursor (curve a) withCa/Al/Fe3O4 magnetic composite catalyst precursor (curve b), there

both existed four mass losses at 60120 C, 190280 C, 350450 Cand 610690 C respectively. The rst mass loss corresponded tothe loss of absorbed water at precursor surface. The second massloss at 190280 C was extremely clear, which assigned to the lossof crystal water of calcium aluminate. The mass loss of constitutionalwater with the form of OH at 350450 C resulted in the change ofthe crystal structure from Ca3 Al2 (OH) 12to Ca12Al14O33and CaO,and the mass loss at 610690 C was due to the catalyst sintering.

The results of the thermal analysis suggested that the proper cal-cining temperature of magnetic solid base catalyst was in therange of 450610 C. In this work, the calcining temperature wasstudied from 450 C to 800 C at the molar ratio of Ca to Fe of5:1 and calcining time of 6 h. And the optimum calcining temper-ature was 600 C.

3.4.2. XRD

The XRD patterns of pure calcium aluminate catalyst, as-synthesized Ca/Al/Fe3O4 catalyst, as-calcined Ca/Al/Fe3O4 catalystand commercial grade Fe3O4are shown inFig. 7. By X-ray diffractionanalysis, as-synthesized Ca/Al/Fe3O4 catalyst had the characteristicpeaks of Ca3Al2(OH) 12cubic crystal because the position and rela-tive intensity of the main peaks matched those from the JCPDS card(24-0217) for Ca3Al2 (OH) 12 well. After calcined at 600 C, newphases were observed in the corresponding XRD pattern. The peaks

of 2values at 18.1, 27.8, 29.7, 33.3, 35.0, 41.1, 46.5, 57.1, 66.8, 71.8were the characteristic peaks of mayenite (Ca12Al14O33) crysta(JCPDS Card No. 48-1882) and peaks of 2values at 32.2, 37.3, 53.9were indexed as cubic CaO (JCPDS Card No. 37-1497). The mainphase of as-calcined magnetic composite catalyst was mayenite(Ca12Al14O33). Seen fromFig. 7, the as-calcined magnetic compositecatalyst had the characteristic peaks of Ca12Al14O33, CaO and Fe3O4(marked with arrows inFig. 7).

Fig. 4.Recovery rate and lifetime comparison of pure calcium aluminate catalyst and

Ca/Al/Fe3O4magnetic composite catalyst.

Fig. 5. FAME yield with reaction time at ve recycles catalyzed by Ca/Al/Fe3O4 magneticcomposite catalyst.

Fig. 6.The TG curves of pure calcium aluminate catalyst precursor (a) and Ca/Al/Fe3O4

magnetic composite catalyst precursor (b).

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In XRD patterns of as-synthesized magnetic catalyst, the ve dif-fraction peaks have been assigned to the characteristic reections ofFe3O4. It can be concluded that Fe3O4nanoparticles have been em-bedded in/on the as-synthesized catalyst. The pattern of the as-calcined magnetic catalyst not only had the characteristic peaks ofFe3O4, Ca12Al14O33 and CaO, but also appeared new characteristicpeaks of -Fe2O3 at 2=38.1, 54.2. It suggested that parts ofFe3O4have been oxidized to -Fe2O3 after calcination at 600 C for6 h.

Moreover, according to Scherer formula D=0.89/cos, the av-erage particle diameter of pure calcium aluminate catalyst and as-calcined Ca/Al/Fe3O4 magnetic catalyst were calculated to be47.42 nm and 31.51 nm respectively. It suggested that the compositecatalyst supported by Fe3O4nanoparticles had smaller grain size.

3.4.3. SEMThe SEM images of the calcined catalysts with/without magnetic

nanoparticles areshown in Fig. 8.Seenin Fig. 8a), thecalcium aluminatecatalyst was formed by large particles because of the catalyst agglomer-ation at high temperature. However, the magnetic composite catalystshowed some differences in particle size and morphology with calciumaluminate catalyst as observed in Fig. 8b). It was obvious that the

particles of themagneticcomposite catalyst were smaller andmore reg-ular than those of calcium aluminate catalyst and less agglomerationhappened in the magnetic catalyst. It's speculated that the addition ofFe3O4magnetic nanoparticles has effects in decreasing the agglomera-tion in some degree.

3.4.4. BET

By BET measurement, the specic surface area of the magnetite

was 62.21 m2/g and that of pure calcium aluminate catalyst was21.29 m2/g. Furthermore, the BET specic surface area of magneticcomposite catalyst prepared under the optimum condition was25.89 m2/g, which was larger than that of pure catalyst attributed tothe addition of Fe3O4nanoparticles with large specic surface area.The larger specic surface area of the magnetic composite catalystcan give a reasonable explanation why the higher catalytic activityand product yield in the transesterication reaction of biodieselhave been achieved with this magnetic catalyst mentioned inSection 3.1.

3.4.5. EDS

EDS spectra analysis for the magnetic composite catalyst showed

that the catalyst consists of Ca, O, Al and Fe elements. According tothe EDS analysis (seen inTable 1), the molar ratio of Ca to Fe was15:1, which was higher than the actual ratio of Ca to Fe (5:1) in thepreparation. It indicated that not all the Fe3O4 nanoparticles usedhave been embedded in/on the catalyst. Furthermore, not uniformdistribution of Fe3O4 nanoparticles in the catalyst maybe anotherreason for the discordance between the analysis data and experi-mental data.

3.4.6. VSM

Fig. 9shows magnetic hysteresis loops of the Fe3O4particles andmagnetic composite catalyst measured at room temperature byVSM. The Fe3O4particles exhibited superparamagnetic behavior andthe saturation magnetization was about 57.85 emu/g. In comparison,

the saturation magnetization of the Ca/Al/Fe3O4 composite catalystwas about 6.34 emu/g, which was higher than that of Ca(OH)2Fe3O4catalyst (b1 emu/g) reported in Ref. [30]. This was just the reasonwhy the recovery rate of our catalyst was higher than the data in thisreference. With the aid of the forcing magnetic eld, for example, asolid magnet, this magnetic composite catalyst developed in our studycan be separated more easily and completely.

Fig. 7. XRD patterns of pure calcium aluminate catalyst, as-synthesized Ca/Al/Fe 3O4magnetic catalyst, as-calcined Ca/Al/Fe3O4 magnetic catalyst and commercial gradeFe3O4.

Fig. 8.SEM image of pure calcium aluminate catalyst (a) and Ca/Al/Fe 3O4magnetic composite catalyst (b).

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4. Conclusion

In summary, calcium aluminate solid base catalyst was developedand furthermore a magnetic composite catalyst was prepared byloading calcium aluminate onto Fe3O4nanoparticles with a chemicalsynthesis method under the proper conditions of the molar ratio ofCa to Fe 5:1, calcining temperature 600 C and calcining time 6 h.XRD showed the composite catalyst has the characteristic peaks ofCa12Al14O33, CaO and Fe3O4. Comparing the two catalysts without/with magnetic nanoparticles, the Ca/Al/Fe3O4 magnetic compositecatalyst had smaller size and higher specic surface area. As a result,the magnetic composite catalyst had higher catalytic activity andcan lead to a higher product yield 98.71% in the transestericationof biodiesel. Furthermore, it was more convenient and thorough toseparate the prepared Ca/Al/Fe3O4 magnetic composite catalystfrom the reactant mixture with a solid magnet, so the recovery rateof the catalyst was higher than that of the calcium aluminate catalyst.After 5-times use, the biodiesel yield was more than 90% and the re-covery rate was about 87% for the Ca/Al/Fe3O4magnetic compositecatalyst.

The addition of magnetic nanoparticles helps the dispersion of thesolid catalyst and supplies more sufcient contact area between thereactants and catalyst. Besides, the magnetism of the catalyst helpsthe separation from the reactant mixture. This work gives a signi-cant approach to the application of magnetic nanoparticles and canbe attempted to extend to other catalyst systems.

Acknowledgment

This project was nancially sponsored by the Scientic ResearchFoundationfor theReturned Overseas Chinese Scholars,State EducationMinistry, by the National Natural Science Foundation of China(20776107) and Innovation funding of Tianjin University.

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Table 1

EDS analysis of Ca/Al/Fe3O4magnetic composite catalyst.

Element Wt.% At%

OK 24.75 41.89AlK 24.64 24.73CaK 46.26 31.26FeK 4.35 2.11Matrix Correction ZAF

Fig. 9.Magnetic hysteresis loops of commercial grade Fe3O4and Ca/Al/Fe3O4magnetic

composite catalyst.

http://localhost/var/www/apps/conversion/tmp/scratch_9/image%20of%20Fig.%209

study on preparation kf_cao_fe3o4(1)

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